Rai Way is Italy’s DTT transmission tower operator, a unit of the state broadcaster Rai, which has just gone public. It operates a Video Broadcasting – Terrestrial (DVB-T) distribution network serving thousands of transmitter locations via terrestrial and satellite infrastructures. But it also owns the country’s national terrestrial contribution network, based on fiber and microwave, which provides 24/7 high capacity, high quality of service (QoS) connectivity for all studios and other major content acquisition locations in Italy.
Function of the Terrestrial Contribution Network
The quality of video and audio signal transmission has to be higher for contribution than distribution for broadcasting and that is the case with Rai Way’s network. Content is contributed in the highest quality possible prior to distribution in order to ensure an optimum audio-visual experience for the end-user, typically the TV viewer. Rai Way’s new network will upgrade contribution signal quality further by using Net Insight’s lossless Nimbra platform, which will be used to transport all video services. This delivers compressed video over JPEG2000 with full redundancy.
Motivation for IP/MPLS Transport
Until now Rai Way’s terrestrial contribution transmission infrastructure has been based on standards-based proven broadcast technology that was selected a decade ago in 2005. The synchronous technology chosen, synchronous digital hierarchy (SDH), is well known to provide the satisfactorily high QoS, high availability and long-term reliability that all public service operators require. Additionally, by implementing generic framing procedure - framed (GFP-F) mapping of DVB- asynchronous serial interface (ASI) signals, Rai Way is able to overcome the common limitations around mapping services to SDH’s inflexible VC (virtual container) sizes.
However a number of technology trends and new business requirements have emerged since the successful implementation of the SDH network in 2005. Vendor equipment throughout the production workflow, from cameras to media gateways to video routers, increasingly interoperates physically at the Ethernet interface. Service management, new non-linear and remote-live workflows, as well as traditional transmission workflows, can all practically converge at the IP layer. To facilitate a quicker turnaround response to new and novel service requests, the move to an on-demand service environment is necessary, avoiding the need to reserve network capacity.
This “service convergence” strategy, together with a predicted increase in demand for more data services from traditional contribution service operators, meant that Rai Way needed a new IP-centric solution architecture. A more forward-looking terrestrial contribution network will be able to provide a much broader suite of services, in line with today’s modern telecom industry. To achieve this, Rai Way is building a single network capable of transporting a full suite of services required by the production, broadcast and IT departments. This will require balancing core broadcast functions, such as high QoS media transmission, with emerging business requirements, notably the ability to cope with contention and loss-based transport service to reduce costs.
In 2014, Rai Way ultimately selected another standards-based and proven telecoms technology, MPLS, as its transport layer. MPLS will offer Rai Way the functional capacity to fulfil virtually any future service request, while also offering the operator the benefit of a well-known, proven and globally deployed technology.
Unlike mixed-priority traffic in the SDH domain that will have only one flat QoS level, the same mixed-priority traffic in the MPLS domain can be arranged into multiple levels with QoS TE (traffic engineering). Without implementing robust and scalable QoS TE, a contribution service operator cannot expect to leverage an over-subscribed infrastructure service model through effective prioritization. Therefore, when selecting companion technologies alongside the IP/MPLS routers, Rai Way designed the complete system, including the service provisioning and service level agreement (SLA) monitoring, with special attention to this critical QoS TE task.
By deciding to implement its own MPLS network over leased lines, Rai Way is 100 percent independent and in full control of the TE QoS project. It means all future service requests can be handled. Given that these requested new services are likely to be IP based in future, they will be quickly and easily implemented via MPLS.
Rai Way MPLS Contribution Network Architecture
Connectivity Characteristics of the IP/MPLS Network
The IP/MPLS router network is interconnected by point-to-point dual path services (primary and secondary path design). Dual path architecture allows Rai Way to leverage service-level protection technologies such as hitless 1+1, dynamic route re-allocation and service pre-emption, without reserving backup capacity all the time. The geographical connectivity can potentially be provided by any mix of service providers throughout the lifetime of the project.
Service provider connectivity can then primarily be offered point-to-point. In terms of capacity, these could be lambda-based wavelength division services, with capacity limit dependent upon the router network owned by Rai Way, or otherwise 1 Gbps or 10 Gbps services delivered with strict 100 percent throughput guarantees from the service provider. The current network provides a dual path backbone where each core path is 10 Gbps and each regional path is 1 Gbps.
The current network architecture is based on a fixed proportion of the transmission capacity of the core 10 Gbps and regional 1 Gbps links being totally reserved and guaranteed for the use of real-time video. At this time, the majority of the capacity will be reserved for real-time video services use but that can change.
The new network has been built by renovating the previous generation’s transmission, adaptation, encoding, management and control systems:
- IP/MPLS Routers
- Media Gateway for DVB-ASI and serial digital interface (SDI) adaptation to IP
- Umbrella management and control for the complete integrated system
- JPEG200 compression (integrated in the media gateway)
The media gateway is the inter-domain (broadcast and telecoms) technology and provides the protocol/format adaptation from ASI, SD-SDI, HD-SDI and 3G-SDI to IP. Additionally, the media gateway device also performs integrated JPEG200 compression of any format SDI signal. The JPEG200 technology used (10-bit 4:2:2) offers a lossless compression mechanism at significantly lower bandwidth ranges than uncompressed SDI.
Three systems must be engineered to interoperate 100 percent coherently. This includes IP/MPLS routers and media gateways for DVB-ASI and SDI adaptation to IP, as well as umbrella management and control for the complete integrated system. This will offer contribution services instantly on-demand with QoS guarantees.
Between the MPLS router, media gateway and the umbrella management system, a service aware media network (SAMN) overlay on MPLS transport has been created. Between the MPLS network and media gateway locations a dedicated forwarding class (e.g. EF46 to AF41) is assigned. This forwarding class will have a maximum dedicated reserved capacity at all times equal to the predicted peak demand requirements for that TE-engineered link. The media gateway device exclusively performs protection for services in the “SAMN forwarding class.” Finally, all media gateway devices and MPLS routers forward service and label-switched path (LSP) data to the umbrella management system for comprehensive SLA monitoring along with rapid fault detection and resolution.
Rai Way’s new network will allow for the systematic on-demand creation and SLA monitoring of real-time video services, both point-to-point and point-to-multipoint. It will also enable ASI, SDI or JPEG2000 services to be protected or non-protected using a hitless 1+1 mechanism offering 100 percent service availability in the event of path failure. Services may be routed point-to-point or point-to-multipoint according to pre-defined selectable routes or using any available free-routed capacity to the destination at that instance.
Using a standards-based media network overlay approach Rai Way’s new terrestrial contribution network is a marriage of the traditional guaranteed QoS transport network with the over-subscribed multi-layered-QoS IP-service model.
Damien Nagle is technical sales architect at Net Insight with responsibility for media network design and support.
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